Hot acid neutralization of regenerated cellulose containing fabrics treated with alkaline swelling agents



Patented June 29, 1954 UNITED STATES rarer OFFICE AGENTS ChristianBoner, Chur, Switzerland N 0 Drawing.

Application March 1, 1951, Serial No. 213,477. In Switzerland December30, 194.4

Section 1, Public Law 690, August 8,1946 Patent expires December 30,1964 9 Claims.

The present invention relates to improvements in the refining treatmentof textiles containing regenerated cellulose fibers in which suchtextiles are subjected to a swelling treatment with an aqueous solutionof caustic alkali to modify the appearance, texture and hand of thetextile.

It has long been established that alkaline swelling agents react in atotally diiferent manner on regenerated cellulose than on naturalcellulose. Where-as, for example, the known refining effects ofmercerization are obtained with alkaline swelling agents on cotton withor without tension, these alkaline swelling agents have a far moreradical effect on regenerated cellulose whether it be in the form oflong spun fibers or filaments, or in the form of staple fibers and suchswelling agents tend to cause a decided parchmentization which can evenlead to a structural modification of the regenerated cellulose and inany event, lead to an undesirable hardening, stifiening and swelling ofsuch fibers. The effects obtained with regenerated cellulose are ofsubstantially no practical use and, therefore, ways and means have beensought for to elimi nate the drawbacks mentioned in order that treatmentof regenerated cellulose with alkaline swelling agents could be employedto provide utilizable effects, particularly in the mercerization ofmixed fabrics made of cotton and regenerated cellulose.

In accordance with the invention, it has been unexpectedlydiscoveredthat the drawbacks mentioned can be avoided in the refining of woven orknitted fabrics containing regenerated cellulose fibers with alkalineswelling agents and that interesting and valuable refining effects canbe obtained if directly after the treatment with hot or cold alkalineswelling agents, and without any intervening alteration in theconcentration of the alkaline swelling agent on the fabric, su'cnfabricis subjected to an after-treatment with a dilute aqueous solution of anacid at an elevated temperature between 45 C., preferably 50 C., and theboiling point of such acid solution, said acid solution being at leastof such quantity and concentration that the free alkali retained by thefabric is chemically combined and thereby neutralized whereby a suddenneu tralization of such alkali is achieved.

The reasons for the novel improved effects which are obtained with thedirect hot acidifi cation in accordance with the invention, are notcompletely. understood. However, the effects obtained are amazing andthe'differences over the effects obtained with processes employing "the2 same-alkaline swelling concentrations and conditions followed by thehot or cold rinses or the cold acidification previously employed are sogreat as to be visible at a glance.

The acid after-treatment in accordance with the invention, is carriedout with hot dilute solutions of organic or inorganic acids. Theconcentrations employed are such that they do not act as swelling agentson the fibers treated, but only act to neutralize the alkaline swellingagents previously'applied. The acid solutions employed can also contain.other dissolved sub-- stances which are not destructive to the fiber.

For example, such acid solutions can contain 1 quantities of neutralsalts such as sodium sulfate or acid salts of polybasic acids such assodium bisulfate of which the latter still contains a half a mol ofsulfuric acid available for neutralization. The salts mentioned would,of course, occur inherently when dilute sulfuric acid is employed forthe after-treatment in accordance with the invention. Sulfuric,hydrochloric, acetic, formic, oxalic acids and the like are particularlysuitable for the acid treatment. The dilute acid solutions of aconcentration between 3% and 25%, preferably between 3% and 10% aresuitable for the acid after-treatment in accordance with the invention.The goods must remain in contact with the acid at least until the freealkali present in the fibers has been combined and neutralized.

It is of particular advantage to spray the acid solutions evenly overthe goods to be treated to insure that the goods continuously come incontact with fresh solution. However, the goods can also be passedthrough a bath of such solution.

The preliminary treatment of thetextiles containing regeneratedcellulose with alkaline swelling agents can be carried out in the usualway, either with hot-or cold alkali and can be, if desired, preceded orsucceeded by other types of swelling treatments, for example, with acidswelling agents or further treatments with al a-- line swelling agents.

The directacidification at higher temperatures in accordance with theinvention must occur directly after each alkaline swelling treatmentwhether such treatment is employed alone or in combination with otherrefining steps with swelling agents such as acids, organic bases, orinor- 'ganic salts, for example, zinc chloride, ammonial copper oxides,calcium thiocyanate and the like of the required concentration. Thecombined treatments can be repeated, interchanged or appliedalternately. However, the refining treatments with swelling agents otherthan the swelling with alkaline swelling agents cannot be carried outsimultaneously with the hot acidification which, in accordance with theinvention, directly succeeds the alkaline swelling treatment. In otherwords, if, for example, a transparentizing treatment with sulfuric acidof transparentizing strength is contemplated, such transparentizingtreatment is carried out as a step which is distinct from the hotacidification with dilute acids.

The treatment with alkaline swelling agents which precedes the hotacidification in accordance with the invention can be carried out in theusual way with caustic alkalis such as sodium hydroxide, potassiumhydroxide and the like. Usually solutions of sodium hydroxide arepreferred in view of their lower cost. The alkaline swelling agents maybe applied to the textiles with or Without tension, depending upon theeffect desired. The time and temperature of the treatment, as well asthe concentration of the alkali also depend upon the effect desired. Inpractice of the invention, it has been found, for example, thatexcellent results are obtained in accordance with the invention withalkaline swelling treatments with aqueous caustic alkali solutionsequivalent to sodium hydroxide solutions of concentrations rangingbetween about 15 B. and 36 B. at temperatures between 10 C. and theboiling point of the solution, preferably between l C. and 75 C. Theduration of such treatment can be from a few seconds to about 40minutes, preferably from about seconds to about 3 minutes.

The effects obtainable in accordance with the invention can also beinfluenced by selection of temperature and acid employed in the hotacidification. Generally, the higher the temperature of the hot diluteacid solution employed the clearer, softer and more transparent theeffect obtained. Temperatures between about 70 C. and 85 C. have beenfound well suited for the hot acidification. Furthermore, a treatmentwith 5% acetic acid at 85 C. gives a far softer and more brilliantfinish than 5% sulfuric acid at the same temperature.

The duration of the hot acidification treatment is not critical exceptthat it must be sufiicient to effect the complete neutralization of allof the alkali contained in the fabric. Treatments of longer durationthan that required for the neutralization can of course be employed, butthey serve no particular purpose, as the treatment is completed when thetotal neutralization has been accomplished. For practical purposes,periods between 10 and 60 seconds suffice.

The textiles treated in accordance with the invention can be composed ofregenerated cellulose in the form of long spun filaments or fibers or inthe form of staple fiber, either alone or in combination with othertextile materials as mixed yarns or weaves. The textiles treated arepreferably in the form of knitted or woven fabrics. The term regeneratedcellulose as employed herein is intended to embrace viscose artificialsilk, cuprammonium artificial silk, dinitrated collodion silk orcellulose hydrate artificial silk. The other components which can bepresent in the mixed weaves, the mixed yarns and the like can be eitheranimal or vegetable fibers, ester or ether silks, or polymerized orsuperpolymerized fibers such as nylon, and the like.

Depending upon the type of textile refined in 4 accordance with theinvention and the conditions under which the process is applied, one canobtain stiffened fabrics, opal effects, transparents (organdies),imitation wools or linen finishes and the final result can be apatterned fabric, if before the refining process patterned reservesagainst the swelling agent are printed on such fabric. Mixed fabrics ofregenerated cellulose and cotton (unbleached cotton) can also bemercerized with caustic alkali solutions of mercerizing strength incombination with the aftertreatment according to the invention withoutinjuring the regenerated cellulose contained therein.

The following examples serve to illustrate the manner in which theprocess in accordance with the invention can be carried out.

Example 1 A muslin of staple fiber regenerated cellulose under tensionwas impregnated with an aqueous 25 B. NaOH solution for 1 minute at 15C. and then immediately treated with a 5% acetic acid solution until allof the free alkali was neutralized. The fabric was then rinsed, washedout and tentered. This resulted in a fine springy supple regeneratedcellulose staple fiber fabric with a very clear homogeneous transparentappearance.

When such treatment was modified by interposing a rinse with waterbetween the alkaline treatment and the acidification, a hard, strawyagglutenated parchment-like material which was entirely useless, wasobtained.

Example 2 A mixed cotton and viscose weave was impregnated under tensionwith 32 B. at 8 C. for 25 seconds and then immediately acidified with 5%acetic acid at 85 C. This resulted in the mercerization of the cottoncomponent of the fabric to produce a beautiful sheen, and increasedaffinity for dyes and a full organic touch.

The same result was obtained when the 5% acetic acid was replaced by 5%sulfuric acid.

Example 3 A regenerated cellulose staple fiber muslin was printed with agum reserve and then impregnated with 32 B. NaOH at 60 C. for 25 secondsand immediately thereafter acidified with 5% sulfuric acid at 75 C.After this, the fabric was washed and tentered. This treatment produceda patterned regenerated cellulose staple fiber transparent fabric inwhich the reserve portions still have their original properties,

A regenerated cellulose staple fiber muslin was impregnated with 16 B.NaOH at C. for seconds and immediately thereafter acidified with 5%acetic acid at 85 C. and then thoroughly washed out.

This treatment produced an opaline fabric of a woolly character.

Example 5 A muslin of long spun and staple fiber regenerated cellulosewas impregnated with 23 B. NaOH at 10 C. for 35 seconds and thenimmediately acidified with 5% sulfuric acid at C., washed out andtentered. The treatment resulted in a greatly improved and more aeea ieshomogeneous fabric of a more linen-like aspect.

It is to be understood that the invention is not limited. to the aboveembodiments wli .h have been given by way of example, but that bracesall processes in which a rennng t merit of a textile material containingregenerated cellulose fibers is directly followed with a treatment withdilute acid solution at a ture above 415 C. whereby a sudden. shock-loreneutralization of the alkali retained in the tile is obtained uponcontact with such acid solution.

The non-swelling acidifying liquors employed for the after treatment mayalso contain other substances as long as they do not deleteriouslyaffect the textile treated. For example, textile assistants forhumecting, impregnating, softening or rendering the textiles waterrepellent a the like or fillers or dyes may be incorporated in suchacidifying liquors.

The term dilute aqueous solution of an as used herein with reference tothe hot acidic after trea'rnent of the alkali treated textiles isintended to cover solutions of acids of such dilution that they possesssubstantially no swelling or transparentizing effect upon theregenerated cellulose.

This application is a continuation-in-part of my prior application, Ser.No. 639,900, filed January 8, 1946, now abandoned.

I claim:

1. A. process for the treatment of textile containing a substantialquantity of ed cellulose fibers which comprises the steps ofimpregnating said textile with an aqueous NaOlI solution of apredetermined concentration between as. and 3 as. to produce swellefiect upon textile, and, before llaO. solution eiiects parchmentizationand able hardening of the regenerated cellulose ii contained in saidtextile, contacting said imnr nated textile containing said aqueoussolution of NaOH of predetermined concentration with an aqueous solutionof an acid containing a suiiicient amount of acid to combine chemicallywith all of the free alkali contained in the textile, said acid being ofconcentration of about 3% to at a temperature betwen 4:5 C. the boilingpoint of said acid solution until all of the free alkali contained inthe textile is neutralized, whereby a sudden neutralization of all ofsaid free alkali is obtained and its swe action is is minated beforeparchm ation and undesirable stiffening of the re e. ated celluloseiibers contained in said textile Qfl'zC-t" ed, and removing the acidfrom the textile to terminate the treatment of said textile with theaqueous solution of the acid before the contained. therein can effectacid transparentization.

2. The process of claim 1 in which said treatment with th aqueous acidsolution is effected at a temperature between C. and the boiling pointof said acid solution.

3. The process of claim 1 in which said treatment with the aqueous acidsolution is effected at a temperature between 70 C. and 85 C.

4. The process of claim 1 in which said treatment with the aqueous acidsolution is effected while the textile is under tension.

5. The process of claim 1, in which said acid is sulfuric acid.

6. The process of claim 1, in which said acid is acetic acid.

7. A process for mercerizing the cotton content of a textile containingcotton and a substantial quantity of regenerated cellulose fibers whichcomprises the steps of impregnating such textile with an aqueoussolution of NaOI-I of predeterm ned concentration between 15 B. and 36Be. to mercerize the cotton content thereof, and then, before said NaOHsolution efiects parchmentization and undesirable hardening of theregenerated cellulose fibers contained in said textile, contacting saidimpregnated textile conta n solution of the caustic alkali ofpredetermined concentration with an aqueous solution of an acid of about3% to 25% concentration at a temperature between 45 C. and the boilingpoint of said acid solution containing a sufiicient amount of acid tocombine chemically with all of the free alkali contained in the textileuntil all of the free alkali contained in the textile is neutralizedwhereby a sudden neutralization of all of said free alkali is obtainedand its swelling action is terminated before parchmentization andundesirable stifiening of the regenerated cellulose fibers in saidtextile is effected, and removing the acid from the textile to terminatethe treatment of said textile with the aqueous solution of the acidbefore the acid contained therein can effect acid transparentization.

8. A process for the treatment of a textile containing substantialquantity of regenerated cellulose fibers which comprises the steps ofimpregnating such textile with an aqueous NaOH solution of apredetermined concentration between 15 Be. and 35 Be. for a periodbetween 5 seconds and 3 minutes at a temperature between 10 C. and 75 C.to produce a swelling effect upon said textile and then, before saidNaOH solution effects parchmentization and undesirable hardening of theregenerated cellulose fibers contained in said textile, contacting saidimpregnated textile containing said aqueous NaOH solution of thepredetermined concentration with an aqueous 3% to 25% solution of anacid at a temperature between 45 C. and the boiling point of said acidsolution containing a sufficient amount of acid to combine chemicallywith all of the free alkali contained in the textile until all of thefree alkali contained in the textile is neutralized whereby a suddenneutralization of all of said free alkali is obtained and its swellingaction is terminated before parchmentization and undesirable stiffening0f the regenerated cellulose fibers in said textile is effected, andremoving the acid from the textile to terminate the treatment of saidtextile with the aqueous solution of the acid before the acid containedtherein can effect acid transparentization.

9. The process of claim 8, in which the concentration of said aqueousacid solution is from 3 to 10%.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,989,098 Lillienfeld Jan. 29, 1935 1,989,099 Lillienfeld Jan.29, 1935 FOREIGN PATENTS umber Country Date 231,352 Great Britain Nov.30, 1927 335,176 Great Britain Sept. 17, 1930 OTHER REFERENCES AmericanDyestuff Reporter, March 8, 1948, page 162.

1. A PROCESS FOR THE TREATMENT OF A TEXTILE CONTAINING A SUBSTANTIALQUANTITY OF REGENERATED CELLULOSE FIBERS WHICH COMPRISES THE STEPS OFIMPREGNATING SAID TEXTILE WITH AN AQUEOUS NAOH SOLUTION OF APREDETERMINED CONCENTRATION BETWEEN 15* BE. AND 36* NE. TO PRODUCE ASWELLING EFFECT UPON SAID TEXTILE, AND, BEFORE SAID NAOH SOLUTIONEFFECTS PARCHMENTIZATION AND UNDESIRABLE HARDENING OF THE REGENERATEDCELLULOSE FIBERS CONTAINED IN SAID TEXTILE, CONTACTING SAID IMPREGNATEDTEXTILE CONTAINING SAID AQUEOUS SOLUTION OF NAOH OF PREDETERMINEDCONCENTRATION WITH AN AQUEOUS SOLUTION OF AN ACID CONTAINING ASUFFICIENT AMOUNT OF ACID TO COMBINE CHEMICALLY WITH ALL OF THE FREEALKALI CONTAINED IN THE TEXTILE, SAID ACID BEING OF A CONCENTRATION OFABOUT 3% TO 25%, AT A TEMPERATURE BETWEEN 45* C. AND THE BOILING POINTOF SAID ACID SOLUTION UNTIL ALL OF THE FREE ALKALI CONTAINED IN THETEXTILE IS NEUTRALIZED, WHEREBY A SUDDEN NEUTALIZATION OF ALL OF SAIDFREE ALKALI IS OBTAINED AND ITS SWELLING ACTION IS TERMINATED BEFOREPARCHMENTIZATION AND UNDESIRABLE STIFFENING OF THE REGENERATED CELLULOSEFIBERS CONTAINING IN SAID TEXTILE IS EFFECTED, AND REMOVING THE ACIDFROM THE TEXTILE TO TERMINATE THE TREATMENT OF SAID TEXTILE WITH THEAQUEOUS SOLUTION OF THE ACID BEFORE THE ACID CONTAINED THEREIN CANEFFECT ACID TRANSPARENTIZATION.